In a turbomachine, air is compressed by a plurality of blade stages disposed axially along the main axis P of the turbomachine, each stage comprising a series of blades disposed around a circumference about said main axis P. Such a stage is known as a bladed wheel. From a circumferential platform centered on the main axis P, the blades extend outwards substantially radially towards an annular casing. The height of a blade is the radial dimension of the blade, i.e. substantially the difference between the radius of the casing and the radius of the platform.
As shown in FIG. 1, which shows a portion of a bladed wheel, each blade 1 of the bladed wheel extends between the radially-outer surface (wall) 81 of the platform 80 and the radially-inner surface (wall) 91 of the casing 90. Since the blade 1 is constituted by a single airfoil, it is referred to as a single-airfoil blade. The radially-inner end 8 of the blade 1 is secured to the platform 80. The radially-outer end 9 of the blade 1 is fastened to the casing 90 if it constitutes a stator vane, and otherwise it is free if it constitutes a rotor blade. The bladed wheel thus has blades 1 lying between said wall 81 of the platform 80 and said wall 91 of the casing 90, which blades may be stator vanes 1 or rotor blades 1.
Each blade 1 possesses a leading edge 2 and a trailing edge 3, with the axis A (axis of the blade) interconnecting these two edges being substantially parallel to the main axis P of the turbomachine. Each blade 1 is curved relative to its axis A so that one of its faces interconnecting its leading edge 2 and its trailing edge 3 is convex (convex face 4), while the other face interconnecting its leading edge and its trailing edge is concave (concave face 5).
The number of blades on a bladed wheel is determined as a compromise between obtaining low weight for the bladed wheel, obtaining high mechanical strength for a blade (when subjected to thermal stresses and to mechanical stresses due to the bladed wheel rotating at high speed), and maximizing the aerodynamic efficiency of a blade, and consequently the aerodynamic efficiency of the bladed wheel. At present, the geometry of blades does not enable any significant improvement to be achieved in the aerodynamic performance of a bladed wheel carrying such blades.